Demand is growing for gearboxes designed with hybrid propulsion in mind, as owners seek to cut fuel consumption and emissions
A new generation of gearboxes are being developed for two- and four-stroke engines to meet the requirements of hybrid propulsion systems.
These units can be installed on new ships or retrofitted to existing vessels, helping reduce fuel consumption, engine load and running time and emissions.
Executives from two gearbox manufacturers outlined the latest developments in this area during Riviera’s recent Gearboxes: gearing up for hybrid propulsion applications webinar.
During the event, held on 22 February 2021 and part of Riviera’s Marine Propulsion Webinar Week, RENK sales and project engineer for marine propulsion systems Dominik Elskamp discussed the benefits of hybrid gearboxes for two-stroke engines.
He was joined on a panel by Katsa gearbox business sales manager Mikko Happonen, who outlined the latest gearbox technology for four-stroke engines.
The discussion looked at typical hybrid applications involving power take in and take out (PTI/PTO) motors when combined with marine engines and generator sets.
Mr Elskamp introduced the RENK MARHY and Integrated Front-end Power System (IFPS) gearboxes for two-stroke engines during the webinar.
MARHY is a geared PTO/PTI/PTH (power take hybrid) system, mounted on the propulsion shaft line. It can come with power ratings between 500-3,000 kW.
RENK MARHY has a propeller shaft clutch and lubricant oil station, frequency converter, elastic coupling and tunnel gearbox.
“Its most important mode is PTO as it is more efficient than using the generator set to improve the Energy Efficiency Design Index of the ship,” said Mr Elskamp.
This energy-generating mode has lower operating costs than using heavy fuel oil and LNG fuel in engines and generator sets for producing ship power. Some of the power from the engine is siphoned off to the switchboard for vessel power requirements. This also reduces maintenance costs due to lower running hours of the gensets.
MARHY also operates in PTI mode, where an electric motor boosts output from the main engine for higher power demands. This has positive ramifications when designing and fitting out ships.
“Ships can be built with smaller engines and supplemented with electrical power from the genset,” said Mr Elskamp.
The PTH mode significantly impacts ship emissions as the main engine is disconnected and power comes from an electric motor and/or genset. “This could be for electric propulsion only in restricted areas, or as redundancy for a single-screw vessel,” Mr Elskamp said.
A RENK MARHY has been installed on a Knutsen OAS small LNG carrier. This 30,000 m³ gas transportation ship was built by Hyundai Mipo Dockyard and is powered by WINGD 5X52 dual-fuel engines producing 6,710 kW at 93.7 rpm. The gearbox can produce 1,000 kW in PTO and PTH modes.
RENK’s IFPS gearbox package includes a geared PTO system on the front of a two-stroke engine. “There are space savings due to the flat and modular design at the front-end of the engine,” said Mr Elskamp.
It is mounted at the engine free end with power ratings of either 500 kW, 1,000 kW, 1,500 kW or 2,000 kW. The gearbox features an elastic coupling, frequency converter and a generator.
The first commercial use of a RENK IFPS will be on chemical and product tankers Stena Bulk has on order from Guangzhou International shipyard in China. These 49,900 dwt tankers will be part of Stena’s IMOII MeMax class of ships.
These chemical carriers are powered by MAN’s 6G50ME-C9.6-LGMIN engines, rated at 7,600 kW of power at 84.4 rpm. IFPS is a 1,000 kW PTO on these tankers.
During the discussion, Mr Happonen outlined developments in the Katsa L350 and L490 gearbox series. These are compact, clutched PTO/PTI gearboxes designed for marine hybrid applications.
“These gearboxes combine two power inputs to one main output with flexible clutch options,” said Mr Happonen.
The two main applications are for driving thrusters on workboats, offshore support vessels and tugs, and for propulsion drivetrains. The L350 has a power range of 200-1,000 kW and the L490 range spans 1,000-2,500 kW.
These gearboxes have an integrated wet running, multi-plate clutch.
“PTO or PTI electric motors can be connected for running either as a generator or as a driving motor,” said Mr Happonen.
“Our standalone hybrid PTO/PTI clutch gearboxes have compact designs enabling the selection of main engine or propulsion gearbox as standard,” he said, adding, “They are easy to handle, assemble and maintain.”
These gearboxes enable hybrid propulsion to be integrated with thruster-based propulsion, reducing emissions from vessels in ports, coastal and inland applications and during deepsea operations. They can be controlled by a vessel master from the bridge.
“PTO mode is more efficient than using the generator set”
Katsa’s hybrid PTO gearbox has a hydraulic clutch dynamic torque up to 16,000 Nm. It has independent oil circulation, with pump and integrated oil sump, hydraulic clutch control system with proportional valves and a clutch protection system with a remote bridge control. These PTO gearboxes also have flexible gear ratios for optimal engine and pump revolutions.
Mr Happonen anticipates higher demand for these hybrid gearboxes as more owners select them for different vessel types to reduce emissions and fuel consumption and increase periods between engine and generator set maintenance.
“Maritime will be going for hybrid as this is the main technical solution for the future,” he said. “We are focusing our research on developing smart hybrid gearboxes and ensuring the electric power fits well with the mechanical side.”
Mr Happonen said most of the applications for Katsa hybrid gearboxes were on newbuild vessels with thruster-based propulsion, although these products are available for retrofits if required.
“Retrofit projects would be challenging because of the limited space in enginerooms,” he said. “This is why we make [gearboxes] as compact as possible.”
Katsa is also developing new winch gears and winch electric powerpacks, incorporating permanent magnet (PM) motor technology. For the marine and offshore sector, these could be used for demanding applications, such as escort winches on tugs.
Still, there has been some reticence among shipowners as regards investing in hybrid propulsion gearboxes for newbuildings.
“Many projects are being postponed as system engineers wait for better electric motor components,” said Mr Happonen.
Many webinar attendees agreed. When asked whether the ongoing rapid development of hybrid systems, electric motors and components is resulting in postponed decision making, 54% agreed and 6% strongly agreed, while 40% disagreed.
In a second poll, attendees were asked whether they agreed that there are technically suitable and reasonably priced marine hybrid PTO gearbox solutions on the market. Of those who responded, 47% agreed, 39% disagreed, 11% strongly agreed and 3% strongly disagreed.
Gearboxes supplied to fast ferry and trawler
Reintjes has supplied gearboxes to a new passenger ferry built for services in Trinidad and Tobago and for a German-based pelagic trawler.
Reintjes was involved in the newbuilding of a ro-pax catamaran ferry for the Trinidad and Tobago government-backed National Infrastructure Development Co.
Ferry APT James was built by Austal at its Vung Tau facilities in Vietnam and classed by DNV. It began service at the start of 2021.
This 94-m vessel transports up to 250 vehicles and 926 passengers at high speeds between the islands of Trinidad and Tobago.
Its power comes from four MAN 16-cylinder 28/330 STC engines. These are connected to four Reintjes VLJ7531 gearboxes, driving KaMeWa 112 S3 waterjets.
APT James has a top speed of 37.5 knots and a cruising speed at full load of 30 knots, enabling it to complete a one-way voyage between the islands in less than three hours.
Reintjes also supplied gearboxes to a new trawler completed by Danish shipbuilder Karstensens Skibsværft for fishing company Kristin Fischereigesellschaft.
At 53.6-m, Kristin operates from Cuxhaven, Germany. This 875-gt vessel is German-flagged and has a moulded beam of 11.2 m.
Its power comes from one Caterpillar MaK 8M25 engine, rated at 2,309 kW and compliant with IMO Tier II emissions requirements.
This drives a Berg MPP850 380-cm diameter propeller through a Reintjes LAF 4555 reduction gearbox. Kristin’s steering and rudder was supplied by Kongsberg Maritime. Assisting in manoeuvring this trawler are two Brunvoll-delivered 400 kW side thrusters.
In addition, there are two Scania DI13 400kW auxiliary engines for onboard power.
There is also a power take-off motor and a Cummins DSG 86 1,200kW shaft generator to provide full power to deck winches.
Gearboxes installed on US inland towboats
Gearboxes are integral part of the propulsion systems on tow and push boats operating on US inland waterways. These vessels typically have a pair of diesel main engines, complying with the US Environmental Protection Agency’s (EPA) Tier 3 emissions requirements, driving Sound propellers through a geared transmission.
Master Marine is building a series of four tugboats for Cooper Group subsidiary Plimsoll Marine for transportation along the Lower Mississippi River. These vessels have twin Mitsubishi 803 HP diesel marine engines developing 600 kW of power at 1,400 rpm and are connected to Twin Disc 5321 gears to drive four-blade stainless steel Sound propellers.
Metal Shark’s shipyard in Bayou LaBatre, Alabama, completed its first steel inland towboat newbuilding in 2020. Stephanie Pasentine, a 36.5-m vessel, was built for Florida Marine Transporters as the first of three towboats. It has two Caterpillar 3512C marine diesel engines, each delivering 1,500 kW of power at 1,600 rpm. These turn stainless steel propellers through Twin Disc MGX5600DR reverse reduction gears.
Twin Disc also supplied gearboxes for towboats built by Steiner Construction for Enterprise Marine Services, the first Billie Ruth was delivered in April 2020, while Maggie Rae was completed in October. These are part of a nine-towboat construction programme at Steiner Construction.
These 36.5-m, 2,690-kW powered tugboats were built to a Farrell and Norton design. They each have a pair of Caterpillar 3512 main engines that turn two Sound Denominator propellers through Twin Disc 5600 reduction gears.
In Texas, Lydia Ann Channel Fleet (LACF) christened Elin Merritt as its first newbuild in Q3 2020. This 23.7-m vessel was built by Diversified Marine and has 1,490 kW of power. It has a pair of Cummins QSK38 main engines driving Sound Denominator propellers through Twin Disc 540 reduction gears.